Also good for marking chalk films

I have in my office a magnetic blackboard foil on the wall and use the pins to leave short notes on it. If you have the pins by first vigorously shaken, they write very clearly and with rich colors, which pleases me well. So far, I could do everything again, wash, but you can still see quite some residues. However, the residues come probably from the pressure that is exerted while writing on the film, color is in any case to see any.